The effects of altertoxins on metabolic communication were studied in-vitro. Purified altertoxin-I (56258323), altertoxin-II (56257591), or altertoxin-III (105579746) prepared from Alternaria- alternata grown on cooked rice were incubated with Chinese-hamster- V79 cells at concentrations of 0 to 5 micrograms per milliliter (microg/ml). The compounds were evaluated for their ability to inhibit gap junction communication in a 6-thioguanine resistance assay. Cytotoxicity was evaluated by determining doses that allowed 70 to 95 percent colony survival. 12-O-tetradecanoylphorbol-13- acetate (TPA) and 4-O-methyl-ether-tetradecanoylphorbol-13-acetate (4OTPA) were used as positive controls. Altertoxin-II was the most cytotoxic, followed by altertoxin-III and altertoxin-I. Altertoxin- I was significantly more disruptive to metabolic communication that 4OTPA at all concentrations; the greatest effect was shown by the 4 and 5microg/ml doses. Altertoxin-I weakly affected metabolic communication compared to TPA. Altertoxin-II and altertoxin-III did not significantly affect gap junction communication. The authors conclude that altertoxins induce dose dependent cytotoxicity and altertoxin-I weakly inhibits metabolic communication. Altertoxins that cause significant cytotoxicity or which interfere with cell to cell communication may adversely affect populations which are exposed to altertoxin contaminated food supplies.